I had been hearing a knocking noise as of late on my lathe which varied directly with the motor / spindle speed. I looked into the motor last weekend and found that my drive pulley on the motor was a bit loose and had migrated towards the end of the shaft. When the lathe was turning, the pulley was wiggling slightly, and that caused some knocking. Some of this I believe was my fault as I had the pulley off a while back to measure it as I was trying to copy the pulley just for the experience. When I reinstalled it, I apparently hadn't put it far enough back on to make sure the set screw lined up with the set screw indent hole.
So, I took the motor out, disconnected the two wires, and tore the motor down. The bearings were definitely shot. I noted the sizes, 6202, both ends, looked everything over. The only real issue I noted was that the inside of the motor mount "box" was very poorly machined. It looked like it had been cut with a fly cutter, and that the cutter had dropped in one spot , making a large circular gouge. I didn't take any pictures, but it was pretty bad. So, I took it to the mill and machine that mounting surface down about .018" until it had it mostly cleaned up. I didn't want to take too much material off so I stopped there. At the same time, I machined the three edges of the box that press against the motor mount plate so that everything was nice and true. I took the same amount off of those three edges to keep everything lined up when reinstalled.
Fast forward to yesterday, I got the new bearings installed and put it all back together. The motor runs nice and clean and there is no knocking noise. I had also noticed that it seemed that he large pulley on the spindle had previously seemed to run out quite a bit. Now, that pulley runs nice and true. It seems that the motor bearings were bad enough that it was causing a fluctuation on the large spindle pulley. That translated into a sort of pulsing sound when I was turning something. All of that is gone now.
I would say that the moral of the story is to check your motor bearings. I know they put good spindle bearings in these machines, but the motor bearings, not so much. My lathe is just under a year old as I got it in January. I didn't expect to have to change these bearings out this soon, but am glad to know how easy it is.
So, I took the motor out, disconnected the two wires, and tore the motor down. The bearings were definitely shot. I noted the sizes, 6202, both ends, looked everything over. The only real issue I noted was that the inside of the motor mount "box" was very poorly machined. It looked like it had been cut with a fly cutter, and that the cutter had dropped in one spot , making a large circular gouge. I didn't take any pictures, but it was pretty bad. So, I took it to the mill and machine that mounting surface down about .018" until it had it mostly cleaned up. I didn't want to take too much material off so I stopped there. At the same time, I machined the three edges of the box that press against the motor mount plate so that everything was nice and true. I took the same amount off of those three edges to keep everything lined up when reinstalled.
Fast forward to yesterday, I got the new bearings installed and put it all back together. The motor runs nice and clean and there is no knocking noise. I had also noticed that it seemed that he large pulley on the spindle had previously seemed to run out quite a bit. Now, that pulley runs nice and true. It seems that the motor bearings were bad enough that it was causing a fluctuation on the large spindle pulley. That translated into a sort of pulsing sound when I was turning something. All of that is gone now.
I would say that the moral of the story is to check your motor bearings. I know they put good spindle bearings in these machines, but the motor bearings, not so much. My lathe is just under a year old as I got it in January. I didn't expect to have to change these bearings out this soon, but am glad to know how easy it is.
